In hard disk drives and other storage media, there are many applications that require a certain ordering of commands to be respected. An example of this is a journaling file system. In these systems a set of operations is performed in an atomic manner to guarantee that the file system is always in a consistent state. To do this the file system first writes a record of the operations to be performed, then performs the operations, and at the end writes a confirmation to the journal that the operations were completed. In this way, if the system crashes before the confirmation is written, the system knows it has to redo the operations. The problem here is that the queuing (or write cache) will reorder the commands and therefore may write the confirmation to the journal before all commands are completed.
The current solution to this problem is to flush the queue before sending the update write operation to the HDD. The drawback of this solution is that constant flushing of the queue (and/or the cache) adversely affects performance (throughput). The present invention recognizes the need to address this problem without necessarily requiring a new type of queuing infrastructure that could require a new interface to the HDD and consequently would require the file systems to be rewritten.
Having made this critical observation, the invention disclosed herein is provided.